Method for detecting masking of one or more satellites, electronic detection device and associated computer program product

Abstract

A method for detecting masking of one or more satellites by an obstacle for a GNSS receiver on board a movable carrier, including receiving, for each one of M satellites, a code pseudo-distance measurement and a variation of carrier pseudo-distances, computing of a definite position of the receiver and a computed position of each satellite, detecting a masking of at least one satellite on the basis of the following operations: computing, at a computation instant and for each satellite, of a computed pseudo-distance and a pseudo-distance reconstructed at a previous time, and detecting masking of at least one satellite by analyzing a magnitude, called residue, computed by applying a least squares algorithm.

The invention claimed is: 
     
       1. A method for detecting masking of one or a plurality of satellites by an obstacle, for a GNSS receiver on a mobile carrier, the method comprising:
 continuous reception, at each acquisition instant and for each of M satellites, of a code pseudo-distance measurement, and a variation of carrier pseudo-distances, M being an integer; 
 computation of a definite position of the receiver and of a computed position of each satellite; 
 detection of a masking of at least one satellite, comprising:
 for each satellite and for each acquisition instant, computation, at an instant of computation, (i) of a pseudo-distance computed from the definite position of the receiver and the computed position of each satellite, and (ii) of a reconstructed pseudo-distance at an earlier instant from the code pseudo-distance and each variation of carrier pseudo-distance between the earlier instant and the instant of computation; and 
 detection of a masking of at least one satellite by analyzing a quantity called residue computed by applying a least squares algorithm, from the measurement of code pseudo-distances at the instant of computation, of the definite positions of the receiver and the computed positions of each of the satellites at the instant of computation and at the earlier instant, the computed pseudo-distances and the reconstructed pseudo-distances. 
 
 
     
     
       2. The method according to  claim 1 , comprising prior to said computation of a pseudo-distance and of a reconstructed pseudo-distance:
 generation at an instant, called instant of generation, of at least one group of N satellites, the satellites of the or each group of N satellites being chosen from the M satellites, N being an integer less than or equal to M; and 
 for the or each group of N satellites, association of an instant of birth preceding the instant of generation from which the GNSS signals from each of the satellites in the group of N satellites were all received uninterruptedly, 
 
       wherein said detection is iterated for each group, and 
       wherein, during said computation of a pseudo-distance and of a reconstructed pseudo-distance, the instant of computation is equal to the instant of generation, and the earlier instant is equal to the instant of birth of the group. 
     
     
       3. The method according to  claim 2 , wherein said detecting comprises for each group, subsequent to said computation of a pseudo-distance and of a reconstructed pseudo-distance:
 if, for at least one group of satellites, the residue is greater than a first threshold, then detection of masking of at least one satellite in the group and reiteration of said computing the residue for each subgroup of the group comprising each satellite of the group except one; and 
 if, for a subgroup, the residue is less than a second threshold, then determination of a masked satellite as being the satellite absent from the subgroup. 
 
     
     
       4. The method according to  claim 1 , wherein said computation of a definite position and a computed position comprises, for each acquisition instant:
 computation of an estimated signal-to-noise ratio; and 
 computation of an elevation angle of each satellite from the definite position of the GNSS receiver and the computed position of that satellite. 
 
     
     
       5. The method according to  claim 3 , wherein said computing the residue further comprises for each satellite group:
 computation of a reconstructed pseudo-distance for each satellite, from the code pseudo-distance at instant of generation and the variations of carrier pseudo-distance between the instant of birth and the instant of generation; 
 computation of a first, a second, approximate solution respectively, of a first, a second linear system respectively, each linear system correspondingly depending on the first and the second computed pseudo-distances, on the code pseudo-distance at the instant of generation and on the reconstructed pseudo-distance; and 
 computation of the residue from the first and second approximate solutions. 
 
     
     
       6. The method according to  claim 2  wherein said generation, said association ( 140 ) and said detection are reiterated periodically. 
     
     
       7. A computer program product including software instructions which, when executed by a computer equipment, cause the computer equipment to implement a detection method according to  claim 1 . 
     
     
       8. An electronic detection device comprising technical means suitable for implementing the detection method according to  claim 1 . 
     
     
       9. The method according to  claim 2 , wherein said computation of a definite position and a computed position comprises, for each acquisition instant:
 computation of an estimated signal-to-noise ratio; and 
 computation of an elevation angle of each satellite from the definite position of the GNSS receiver and the computed position of that satellite. 
 
     
     
       10. The method according to  claim 9 , wherein said generation comprises selecting, for each satellite, GNSS signals at each instant of acquisition for which:
 the signal-to-noise ratio of the GNSS signals coming from the satellite at the instant meets a first criterion, and 
 the elevation angle of the satellite at the instant meets a second criterion. 
 
     
     
       11. The method according to  claim 10 , wherein said generation further comprises:
 generation of a first group comprising the satellites, the GNSS signals from which are selected, during said selecting, since an instant which is the earliest with respect to the instant of generation; 
 generation of a second group from the first group, the second group comprising each satellite of the first group and the satellite, absent from the first group, the GNSS signals from which are selected, during said selecting, since an instant which is the earliest with respect to the instant of generation; and 
 if at least one satellite the GNSS signals from which have been selected during said selection at the instant of generation, is absent from each group already generated, then reiteration of said generation of a second group from the last group generated.